| 摘要 |
1406470 Photo-electric apparatus INTERNATIONAL BUSINESS MACHINES CORP 20 Dec 1972 [4 Jan 1972] 58903/72 Heading G1A In an apparatus for monitoring irregularities on a periodically structured surface 8 in which a laser beam is scanned - from 2a to 2c - periodically across the surface to produce an interference pattern at a photo-cell assembly 9, the intensity of at least one order of interference is sensed. A laser beam is scanned across the surface 8, e.g. of a magnetic storage disc, by an oscillating mirror 5. For a disc of acceptable quality the machine markings on the disc will have a regular, periodic structure, Fig.2 (not shown) and the disc will hence act as a reflection grating. The assembly 9 is positioned such that the -1, 0, +1 orders of interference fall on photo-cells 12, 10, 11 respectively. A photo-cell 14 monitors scattered light, while photo-cell 13 receives the ¢ order of interference. For a regular surface structure the output from photo-cell 13 will be steady and relatively low, Fig.4, left (not shown). However, irregularities in the machine cut, Fig.3 (not shown) will produce a varying, relatively high output from photo-cell 13, Fig.4 right. The scattered light level output from photo-cell 14 will also be greater in the latter case. The entire disc surface is scanned either by rotating the disc or by rotating the optical system about the disc.
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